I've never really looked closely at a 4g. I'm very happy with my 3g. I assumed the screen was slightly larger, but I guess it's hard to tell from online photos. If video plays the same on both, then I would jump on a 3g while they are so heavily discounted.

Having owned both (and still own a 4G), I say get the 3G if you can get it cheaper than the 4G. Although the 4G has a better build quality, there are few advantages to the new form factor, other than viewing photos. Until they release a patch, there's the annoyance of the 4G switching to cover flow while in your pocket and not being able to blindly control it as a result.